std::chrono::year_month_weekday::year, std::chrono::year_month_weekday::month, std::chrono::year_month_weekday::weekday, std::chrono::year_month_weekday::index, std::chrono::year_month_weekday::weekday_indexed

From cppreference.com
 
 
Utilities library
General utilities
Date and time
Function objects
Formatting library (C++20)
(C++11)
Relational operators (deprecated in C++20)
Integer comparison functions
(C++20)(C++20)(C++20)   
(C++20)
Swap and type operations
(C++14)
(C++11)
(C++11)
(C++11)
(C++17)
Common vocabulary types
(C++11)
(C++17)
(C++17)
(C++17)
(C++11)
(C++17)
(C++23)
Elementary string conversions
(C++17)
(C++17)
 
 
 
constexpr std::chrono::year year() const noexcept;
(1) (since C++20)
constexpr std::chrono::month month() const noexcept;
(2) (since C++20)
constexpr std::chrono::weekday weekday() const noexcept;
(3) (since C++20)
constexpr unsigned index() const noexcept;
(4) (since C++20)
constexpr std::chrono::weekday_indexed weekday_indexed() const noexcept;
(5) (since C++20)

Retrieves the field values stored in this year_month_weekday object.

Return values

1) Returns the stored std::chrono::year value.
2) Returns the stored std::chrono::month value.
3) Returns the stored std::chrono::weekday value.
4) Returns the stored weekday index.
5) weekday()[index()].

Example

#include <iostream>
#include <chrono>
 
int main()
{
    std::cout << std::boolalpha;
 
    constexpr auto ym {std::chrono::year(2021)/std::chrono::January};
    constexpr auto wdi {std::chrono::Wednesday[1]};
    auto ymwdi {ym/wdi};
    auto index = ymwdi.index() + 1;
    auto weekday = ymwdi.weekday() + std::chrono::days(1);
    ymwdi = {ymwdi.year()/ymwdi.month()/weekday[index]};
    // Second Thursday in January, 2021
    std::cout << (std::chrono::year_month_day{ymwdi} == 
                  std::chrono::January/14/2021) << '\n';
}

Output:

true